1. Field of the Invention
The present invention relates to a plating film fabrication method, and more particularly to a magnetic thin film head fabrication method. Still more particularly, the invention relates to a magnetic thin film head fabrication method using an electroplating technique in which the composition of an initially formed layer in an upper shield of a magnetic thin film head is precisely controlled. Furthermore, the invention pertains to a magnetic thin film head manufactured by the magnetic thin film head fabrication method, and to a magnetic disk apparatus comprising the magnetic thin film head thus manufactured.
The invention is also applicable as a plating film fabrication method other than the magnetic thin film head fabrication method mentioned above, and it is possible to manufacture electronic circuit substrates using the plating film fabrication method according to the invention.
2. Description of the Related Art
Recently, there has been an ever increasing demand for higher density of recording and higher-rate signaling of data in magnetic disk apparatus. As a magnetic thin film head for use in a magnetic disk apparatus, an integrated head comprising an MR or GMR read head element and an inductive write head element has been developed.
In the magnetic thin film head, it is required to increase BPI (bits per inch) and TPI (tracks per inch) for realizing higher recording density. As the BPI and TPI increase, a read output tends to decrease. With a decrease in the read output, noise-after-write and output fluctuation have a significantly adverse effect thereon to cause a read error.
For realizing higher-rate communication, a write frequency has been shifted to a higher level, causing a tendency to increase noise-after-write.
The term “noise-after-write” used herein signifies a phenomenon in which noise is produced on a read output at the time of reading data recorded on a magnetic disk.
As demonstrated in FIG. 2, evaluation of noise-after-write can be performed in the following manner: A write current having a predetermined frequency is applied for a period of several tens of microseconds, and then after the write current is turned off, noise outputs exceeding a predetermined slice level are counted through a read head output terminal for a period of several tens of microseconds. In the evaluation of noise-after-write exemplified in FIG. 2, a write-read operation was repeated 10,000 times per magnetic thin film head slider, and a magnetic thin film head was judged to be defective if the number of noise outputs was larger than a predetermined value.
The term “output fluctuation” used herein signifies a phenomenon in which a read output amplitude decreases or increases at the time of reading data recorded on a magnetic disk. Since this phenomenon is accelerated by addition of a write operation, output fluctuation dvpp is expressed as shown in FIG. 3:dvpp=|Vpp(MAX)−Vpp(min)|/Vpp(Ave)×100 (%)In the evaluation of output fluctuation exemplified in FIG. 3, a write-read operation was repeated 10,000 times per magnetic thin film head slider, and a magnetic thin film head was judged to be defective if the output fluctuation dvpp was higher than a predetermined percentage (%).
Conventionally, for effective reduction of noise-after-write and output fluctuation in the magnetic thin film head, shield film formation on the upper and lower sides of a sensor film serving as a read element is made in such a fashion that a film thickness of an upper shield and a magnetostriction constant λ representing a magnetic characteristic thereof are controlled. FIG. 4 shows relationships among shield film thickness, noise-after-write, and output fluctuation. As the shield film thickness increases, both the noise-after-write and output fluctuation tend to decrease. The noise-after-write is minimized at a level of 4.5 μm in shield film thickness, and the output fluctuation is minimized at a level of 3.0 μm in shield film thickness. In the range of more than 3.5 μm in shield film thickness, however, read-track and write-track positioning accuracies are decreased on inner and outer tracks of a magnetic disk. Therefore, in consideration of the allowable ranges of noise-after-write and output fluctuation, it is required to provide a shield film thickness of 2.7 to 3.5 μm.
In FIG. 5, there are shown relationships among magnetostriction constant λ, noise-after-write, and output fluctuation. The noise-after-write is minimized in the vicinity of “magnetostriction constant λ=−3.5×10−7”, and appreciably increases in the range of “magnetostriction constant λ≧0×10−7”. The output fluctuation is minimized in the vicinity of “magnetostriction constant λ=−2.0×10−7”. NiFe permalloy used as a shield material has a magnetostriction constant which shifts to the range of +1.0 to +2.0×10−7 in heat treatment taken as a post-process step. Therefore, in consideration of a shift of the magnetostriction constant due to the heat treatment along with the allowable ranges of noise-after-write and output fluctuation, it is required to provide a magnetostriction constant λ of −2.0 to −4.0 ×10−7. Under this condition, “Ni=80.8 to 81.2 wt %” is given in terms of relationship between magnetostriction constant λ and film composition shown in FIG. 6. However, on a plating under-layer film, an initially formed layer of an upper shield film is liable to be Fe-rich, i.e., it has been found that Ni is 78.9 wt % and λ is +4.8×10−7 in an initially formed layer of 0.2 μm in thickness in a case where Ni is 81.1 wt % and λ is −3.5×10−7 in an upper shield film of 3.5 μm in thickness.
In view of the above, it is apparent that the noise-after-write and output fluctuation largely depend on the composition and magnetostriction constant of the initially formed layer of the upper shield film disposed in the vicinity of the sensor film. It is therefore required to improve the upper shield film for achieving higher recording density and higher-rate communication in magnetic disk apparatus.